Approximately 100 million people worldwide suffer from type II diabetes (NIDDM), which is characterized by hyperglycemia due to excessive hepatic glucose production and peripheral insulin resistance, the root causes for which are as yet unknown. Consistent control of plasma glucose levels in diabetes patients may offset the development of diabetic complications and beta cell failure seen in advanced disease.
Plasma glucose is normally filtered in the kidney in the glomerulus and actively reabsorbed in the proximal tubule. Ninety percent of glucose reuptake in the kidney occurs in the epithelial cells of the early 51 segment of the renal cortical proximal tubule. SGLT2, a 672 amino acid protein containing 14 membrane-spanning segments that is predominantly expressed in the early 51 segment of the renal proximal tubules, is likely to be the major transporter responsible for this reuptake. The substrate specificity, sodium dependence, and localization of SGLT2 are consistent with the properties of the high capacity, low affinity, sodium-dependent glucose transporter previously characterized in human cortical kidney proximal tubules. In addition, hybrid depletion studies implicate SGLT2 as the predominant Na+/glucose cotransporter in the 51 segment of the proximal tubule, since virtually all Na-dependent glucose transport activity encoded in mRNA from rat kidney cortex is inhibited by an antisense oligonucleotide specific to rat SGLT2. In humans, mutations in SGLT2 have been associated with familial forms of renal glucosuria, providing further evidence of the primary role of SGLT2 in renal glucose reabsorption. In such patients, renal morphology and renal function is otherwise normal. Inhibition of SGLT2 would be predicted to reduce plasma glucose levels via enhanced glucose excretion in diabetic patients.
Selective inhibition of SGLT2 in diabetic patients could normalize plasma glucose by enhancing the excretion of glucose in the urine, thereby improving insulin sensitivity, and delaying the development of diabetic complications, in the absence of significant gastrointestinal side effects.